Renewable and cost-effective fillers for polymeric materials

ABSTRACT

Polymer composites are provided, and more particularly, polymer composites of ground date pits disposed in a polymer matrix. The composites can be formed by a process of preparing reinforced polymer composites having a fibril melt fracture surface, including blending a mixture of date pit particulate with a thermoplastic polymer; melting the mixture; and forcing the melt through a die to produce the polymer composite having a fibril containing surface.

FIELD OF THE INVENTION

The invention relates to a polymer composite, and more particularly, toa polymer composite of ground date pits disposed in a polymer matrix.

BACKGROUND OF THE INVENTION

Fillers are routinely used by polymer and plastic industry to reduce thecost of end products and to enhance some desired properties, such asphysical and mechanical properties. However, conventional fillermaterials can be costly and therefore need to be processed in anefficient manner, and conventional inorganic fillers, such as aluminiumtrihydroxide and the like may pose environment risks when used aspolymer fillers.

Formulation of biocomposites has been an attractive endeavor forresearchers in the last decade. There are several advantages, eitherenvironmental or economical, of using biocomposites over ordinarycomposites, especially those based on thermoplastics matrices, forvarious applications such as structural and food packaging. Thebiodegradability feature of such composites offers a solution for theproblem of municipal waste management. Besides the biodegradability ofpolymers filled with biomaterials, the availability of these fillers,normally of agricultural residue origin, at very low cost levels makesthe production of these composites economically feasible.

Several biocomposite systems of thermoplastic matrices and bio-fillershave been reported in the literature, wherein various bio-fillers, suchas wheat straw, corncob, rice husk, and sugarcane bagasse wereincorporated with polymer matrices, such as polypropylene, high-densitypolyethylene (HDPE), low-density polyethylene, and polyvinyl chloride.From an economic point of view, incorporating a cost-effective filler ina polymer will only be feasible if it does not drastically alter themain matrix-resin characteristics, such as mechanical properties.

Saudi Arabia is well recognized for its palm trees (Phoenix dactyliferaL.). In addition, Saudi Arabia is among the largest world producers ofdate fruit, 4700,000 MT per year. On the consumption of date fruit as amain daily meal in almost each Saudi dwelling, date pits are usuallydiscarded as materials with no use or value. Nevertheless, thesepresumably designated waste materials, i.e., date pits, containimportant constituents such as oils (up to 10%), minerals (considerablyrich in potassium), and fibers (46.4%) that may be utilized for specificpurposes.

Ghazanfari et al. (“Thermal and Mechanical Properties of Blends andComposites from HDPE and Date Pits Particles”, Journal of CompositeMaterials, 42(1) (2008); pp. 77-89) disclose formulating polymer-datepits composites based on HDPE as the hosting polymer, and conclude thatincorporating date pit flour with HDPE tends to decrease the melt flowindex (MFI), and at the same time increase the thermal conductivity ofthe resulting composites. The date pits investigated by Ghazanfari etal. are of the Abdoulahi cultivar, which demonstrate reductions intensile strength as compared to non-composited (neat) polymer, onincreasing weight percentages of date pit flour in the composites.

U.S. Pat. No. 4,011,130 to Worden discloses waterlaid sheets comprisingessential solids consisting of (I) elastomeric (polyurethane) binder,and (II) nonelastomeric solids comprising inflexible, non-fibrous,rounded, particulate fillers (which may be vegetable flours preparedfrom peach pits, apricot pits and cherry pits) and a fibrous reinforcingcomponent. The waterlaid sheets are useful as substitutes for leather inthe manufacture of footwear, particularly as the outsole or insoleportion of a shoe. However, no comparison of tensile strength betweenthe neat polymer and the polymer composite is provided.

Accordingly, polymer and plastic industries would benefit from ademonstration of affordable, efficient bio-fillers which would reducethe cost of the final products and yet not diminish the strengthcharacteristics of the polymer, as compared to the correspondingnon-composited polymer.

SUMMARY OF THE INVENTION

In a first aspect of the invention, a process of preparing a reinforcedpolymer composite having a fibril melt fracture surface, comprisesblending a mixture of date pit particulate with a thermoplastic polymer;melting the mixture; and forcing the melt through a die to produce thepolymer composite having a fibril containing surface.

In another aspect the invention, composition comprises a mixture of datepit particulate from the fruit of Phoenix dactylifera L., variety khlaasor sekari, and a thermosetting polymer selected from the groupconsisting of epoxies, vinyl esters and polyesters.

In yet another aspect of the invention, a process of preparing areinforced polymer composite, comprises solution blending a mixture ofdate pit particulate from the fruit of Phoenix dactylifera L., varietykhlaas or sekari, and a solution of a thermosetting polymer, andremoving solvent from the solution.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in the detailed description whichfollows, in reference to the noted plurality of drawings by way ofnon-limiting examples of exemplary embodiments of the present invention.

FIGS. 1( a)-(c) show scanning electron micrographs of melt fracturesurfaces of various loadings of date pit particulate in high densitypolyethylene matrices;

FIGS. 2( a) and (b) show scanning electron micrographs of melt fracturesurfaces of various loadings of date pit particulate in polystyrenematrices;

FIGS. 3( a) and (b) show scanning electron micrographs of melt fracturesurfaces of composites of polystyrene, date pit particulates and twodifferent compounding modifiers; and

FIG. 4 shows a graph comparing the Tensile Strengths of various date pitparticulate/high density polyethylene composites at various particulateloading levels.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to composites of polymers filled with naturallyoccurring fillers. More specifically, it has been found that the fruitof dates, i.e. the date pits, can be ground into particulate and blendedwith polymers to form composites having unique surface characteristicsupon melt processing of the composites, without sacrificing the overallstrength characteristics of the polymers, as compared to thecorresponding non-composited polymers.

Advantageously, the processes and products of the present inventionprovide inexpensive, renewable sources for polymer fillers which can actto reduce the overall cost of polymeric articles made from thecomposites, but also provide an avenue for reducing waste from theconsumption of dates, commonly an every-day occurrence in many MiddleEastern households.

In implementing the present invention a mixture of date pit particulatecan be blended with a thermoplastic polymer, the mixture melted, in forexample a melt extruder as is known in the art, and the melt is forcedthrough an extrusion die to produce a polymer composite having a fibrilcontaining surface. Upon examination of the surface using scanningelectron microscopy (SEM), it is found that the surface of the meltprocessed composites demonstrate a unique, fibril-containing meltfracture surface, which can enhance physical characteristics of theextruded polymer compositions, such as toughness and stiffness, ascompared to neat polymers.

In embodiments, the date pit particulate can be particulate from thefruit of Phoenix dactylifera L., variety khlaas or sekari, whichvarieties are commonly consumed in large quantities in Middle Easternhouseholds, such as in Saudi Arabia. The date pits are advantageouslyground or chopped to particulate of an average size of between about0.25 mm and 1.0 mm.

The melt processing according to the present invention can be practicedwith a number of different thermoplastic polymers to form the compositematrix, such as those selected from the group consisting of polystyrene,polyethylene, polypropylene, polyethylene terephthalate, polyvinylchloride, polymethylmethacrylate, polycarbonate,acrylonitrile-butadiene-styrene (ABS) and polyamide. Those skilled inthe art will recognize that many other such thermoplastic polymers canbe melt processed into date pit particulate/polymer composites andarticles, such as molded articles, according to the present invention.

The concentration or loading of the date pit particulate in thecomposite is not particularly limited, and can advantageously be in anamount of between about 1 and about 40 wt % based on the weight of thecomposite. For example when the polymer is high density polyethylene,the composite can contain from 5 wt % to 30 wt % of date pit particulatefrom the variety sekari; or from 10 wt % to 40 wt % of date pitparticulate from the variety khlaas. When the polymer is polystyrene,the composite can contain from 10 wt % to 40 wt % of date pitparticulate from the variety khlaas, or from 5 wt % to 30 wt % of datepit particulate from the variety sekari.

In any event, the polymer composite demonstrates Tensile Strengthvarying no more than about 10% from that of the uncomposited polymer.Unexpectedly, date pit particulate/polymer composites can besuccessfully produced from thermosetting polymers too, such as from thegroup consisting of epoxies, vinyl esters and polyesters.

In this embodiment, a reinforced polymer composite is formed by solutionblending a mixture of date pit particulate from the fruit of Phoenixdactylifera L., variety khlaas or sekari, and a solution of athermosetting polymer, and removing solvent from the solution.Particulate loadings can advantageously be from about 5 wt % to about 40wt %, depending on the date pit particulate/polymer combination.

EXAMPLES Example 1 High Density Polyethylene (HDPE)/sekari (S)Composites

Composites were formulated by melt extrusion where 10 to 40 wt % of datepit particulate was dispersed in a polymer matrix (HDPE). FIG. 1 showsthe morphology of the fractured surface of the blends. It is clearlyseen that some fibril morphology has developed. As far the mechanicalproperties, compounding polymer with date pits particulate did notaffect important properties such as tensile strength (ASTM D-638), evenat relatively high filler content, e.g 40 wt % (FIG. 4).

Example 2 Polystyrene (PS)/Date Pit Composites

Samples of PS/date pit particulate composites were prepared and themorphology of the blends' melt fracture surfaces was studied by scanningelectron microscope (SEM). FIG. 2 shows the morphology of PS/date pitparticulates at 30 wt % particulate loading. The morphology exhibitedsome fibril-like characteristics, and satisfactory adhesion between datepit particulates and polymer matrix.

Example 3 Coupling Agent Composites

Coupling agents and compatibilizers such as isocynate, silane, anddi-phenylmethane were compounded with the polymer/date pit particulatecomposites to enhance the surface morphology. FIG. 3( a) shows effect ofadding di-phenylmethane (DPHM) to the melt fracture surface morphologyof the composite containing 30 wt % K and 70 wt % PS.

Example 4 Toughness Modifier Composites

Toughness modifiers were added to the composites to compensate for thereduction in some properties, such as impact strength using some melatedpolyolefins elastomers (e.g. ethyelene/propylene grafted with maleicanhydride, indicated as EP-g-MA). FIG. 3( b) shows the morphology ofmelt fracture surface of a composite containing 30 wt % K and 70 wt %PS.

The foregoing examples have been provided for the purpose of explanationand should not be construed as limiting the present invention. While thepresent invention has been described with reference to an exemplaryembodiment, Changes may be made, within the purview of the appendedclaims, without departing from the scope and spirit of the presentinvention in its aspects. Also, although the present invention has beendescribed herein with reference to particular materials and embodiments,the present invention is not intended to be limited to the particularsdisclosed herein; rather, the present invention extends to allfunctionally equivalent structures, methods and uses, such as are withinthe scope of the appended claims.

1. A process of preparing a reinforced polymer composite having a fibrilmelt fracture surface, comprising: blending a mixture of date pitparticulate with a thermoplastic polymer; melting the mixture; andforcing the melt through a die to produce the polymer composite having afibril containing surface.
 2. The process of claim 1, wherein the datepit particulate comprises particulate from the fruit of Phoenixdactylifera L., variety khlaas or sekari.
 3. The process of claim 1,wherein the date pit particulate has an average size of between about0.25 mm and 1.0 mm.
 4. The process of claim 1, wherein the polymer ofthe polymeric matrix is a thermoplastic polymer selected from the groupconsisting of polystyrene, polyethylene, polypropylene, polyethyleneterephthalate, polyvinyl chloride, polymethylmethacrylate,polycarbonate, acrylonitrile-butadiene-styrene (ABS) and polyamide. 5.The process of claim 3, wherein the date pit particulate is present inan amount of between about 1 and about 40 wt % based on the weight ofthe composite.
 6. The process of claim 4, wherein the polymer is highdensity polyethylene.
 7. The process of claim 6, further comprising from5 wt % to 30 wt % of date pit particulate from the variety sekari. 8.The process of claim 6, further comprising from 10 wt % to 40 wt % ofdate pit particulate from the variety khlaas.
 9. The process of claim 4,wherein the polymer is polystyrene.
 10. The process of claim 9, furthercomprising from 5 wt % to 30 wt % of date pit particulate from thevariety sekari.
 11. The process of claim 9, further comprising from 10wt % to 40 wt % of date pit particulate from the variety khlaas.
 12. Theprocess of claim 1, wherein the polymer composite demonstrates TensileStrength varying no more than about 10% from that of the uncompositedpolymer. 13-14. (canceled)